1. Field of Invention
Exemplary aspects of the present invention relate to an illumination unit, and a projector including the same.
2. Description of Related Art
Related art projectors include an illumination unit to emit an illumination light, an electrooptic modulation unit to modulate the illumination light from the illumination unit in response to an image signal, and a projection optical system to project the light modulated by the electrooptic modulation unit as a projection image on a projection surface, such as a screen.
In such a related art projector, the luminance distribution of the projected and displayed image may be roughly uniform. For this reason, an illumination unit composed of a so-called integrator optical system, capable of illuminating the illumination area on which an image is formed at a roughly uniform light intensity distribution is used as the illumination unit. See, e.g., JP-A-2002-55208 (FIGS. 1 to 3).
FIG. 13 is a schematic showing a related art illumination unit. FIGS. 14(a)–(c) are schematics for illustrating the integrator optical system in the related art illumination unit. FIG. 14(a) is a perspective view of a first lens array and a second lens array. FIG. 14(b) is a front view of the first lens array. FIG. 14(c) is a schematic showing the image formation area of a liquid crystal device as the electrooptic modulation unit which is the illuminated area. FIG. 15 is a schematic showing the light intensity distribution on the light incident surface of the first lens array in the related art illumination unit.
A related art illumination unit 900 includes a light source unit 910 and an integrator optical system 960 as shown in FIG. 13.
The light source unit 910 has an arc tube 912, an ellipsoidal reflector 914, and a collimating lens 916. Thus, with this configuration, the light radiated from the arc tube 912 is reflected by the ellipsoidal reflector 914, and emitted toward the illuminated area. The light from the ellipsoidal reflector 914 is converted into roughly parallel illumination luminous fluxes at the collimating lens 916, and emitted.
The integrator optical system 960 has a first lens array 920 having a plurality of small lenses 922, a second lens array 930 having a plurality of small lenses 932, a polarized-light converting element 940, and a superimposing lens 950. Thus, with this configuration, the first lens array 920 splits an illumination luminous flux from the light source unit 910 into a plurality of partial luminous fluxes. The plurality of the partial luminous fluxes are superimposed on the image formation area LA of the liquid crystal device by the second lens array 930 and the superimposing lens 950. The longitudinal to transverse dimension ratio of the image formation area LA of the liquid crystal device is, as shown in FIG. 14(c), set as a ratio of longitudinal dimension (Dy):transverse dimension (Dx)=3:4.
This illumination unit 900 enables the implementation of an illumination luminous flux having a roughly uniform light intensity distribution on the image formation area LA of the liquid crystal device even when the light intensity distribution of the illumination luminous flux emitted from the light source unit 910 is nonuniform.
In such an illumination unit, the light radiated from the arc tube is intercepted by the arc tube itself. For this and other reasons, as shown in FIG. 15, an area with an extremely small light intensity (hereinafter “a shadow area”) S occurs at the light incident surface central part of the first lens array. Therefore, in order to achieve an illumination luminous flux having a roughly uniform light intensity distribution on the image formation area of the liquid crystal device, the number of the small lenses in the first lens array may be set at a large value to a certain degree. Whereas, in order to achieve the enhancement of the light use efficiency, and the reduction of the stray light level in the projector, the lens shape of each small lens in the first lens array may be similar to that of the image formation area of the liquid crystal device, and the shape of the first lens array may be a square.
Under such circumstances, in the related art illumination unit 900, as shown in FIG. 14, the first lens array 920 is configured to have 48 small lenses 922 arrayed in a matrix with eight rows by six columns in the transverse direction and in the longitudinal direction, respectively. Whereas, the longitudinal to transverse dimension ratio of each small lens 922 is set at a ratio of longitudinal dimension (dA):transverse dimension (dB)=3:4, and the shape of the first lens array 920 is set to be a square.